1. Field of the Invention
The present invention relates to a disc apparatus having a DC motor which rotates a disc.
2. Description of the Related Art
In a disc apparatus which rotates a disc such as CD, CD-R, DVD or the like by using a DC motor such as a spindle motor to record and reproduce images and so on, dust particles are sometimes generated due to an abrasion of a brush in the DC motor and cause a short circuit of a commutator in the DC motor. When the commutator is short-circuited, the spindle motor stops rotating, and the disc thereby stops rotating. When the disc stops rotating, a controller which controls the disc apparatus increases an output current of a drive IC which drives the DC motor to speed up a rotation speed of the spindle motor. The drive IC produces heat due to the increase of the output current. The heat may cause a malfunction of the drive IC and a large current flowing through an actuator. Moreover, when the disc stops rotating, the controller gets less able to obtain an accurate operation of the actuator. As a result, the controller forces the drive IC to operate to rotate the disc. In this case, the drive IC passes the large current through the actuator and consequently, a cover of the actuator sometimes burns.
In Japanese Laid-Open Patent Publication No. 10-191551, there is a disclosure of a means which detects whether or not an electrical current which flows through a motor goes beyond a predetermined level and judges that the motor is short-circuited when the excess of the electrical current over the predetermined level continues for a predetermined period of time. In Japanese Laid-Open Patent Publication No. 2001-298988, there is a disclosure of a means which detects whether or not a voltage follows a pulse signal in an apparatus which applies the voltage to a motor by making the pulse signal on and off and which judges that the motor is short-circuited when the state that voltage does not follow the pulse, signal continues for a predetermined period of time.
However, in the techniques shown in the above publications, the judgment whether the motor is short-circuited or not is based on the abnormal state of the electrical current and the voltage continuing for the predetermined period of time, so that the techniques enable the detection of the state that the motor is constantly short-circuited, however, they do not enable the detection of the state that the motor is partially short-circuited and the states of short circuit and non-short circuit alternately arise according to the rotation of the motor.
The present invention is to solve the problem described above, and an object of the present invention is to provide a disc apparatus having a spindle motor to rotate a disc which can judge accurately whether or not the spindle motor is at fault due to a short circuit and also prevent the spindle motor from driving in case of failure in the spindle motor due to the short circuit.